Inverse gain modulator

Abstract

In a transponder having first and second antennas an inverse gain modulator is provided. The inverse gain modulator comprises a power-responsive balance circuit coupled to the two antennas. The power level of the output signal returned by the second antenna is inversely related to the power level of the signal received by the first antenna.

What is claimed as new and desired to be secured by Letters Patent of the United States is: 
     
       1. An inverse gain modulator comprising in combination, (a) a directional power separator having input, output and central terminals;   (b) means for receiving input energy connected to the input terminal of said directional power separator;   (c) means for transmitting output energy connected to the output terminal of said directional power separator;   (d) a quadrature hybrid having an input port coupled to said central terminal of said directional power separator, an output terminal terminated in a precision load and biasing input, and first and second other terminals respectively terminated by a varactor diode and a reactance circuit, said varactor diode being biased by said bias input, whereby the amount of power reflected by said quadrature hybrid and coupled by said directional power separator to said output transmitting means is a function of input power.   
     
     
       2. A system according to claim 1 in which a limiter is connected to the input terminal of said directional power separator. 
     
     
       3. A system according to claim 2 in which said limiter comprises a varactor diode. 
     
     
       4. In a circuit for receiving an input signal and for providing an output signal having stronger portions corresponding to weaker portions of the input signal and having weaker portions corresponding to stronger portions of the input signal, the combination comprising: a quadrature hybrid having an input port, an output port and first and second other ports;   a varactor diode connected to terminate said first other port;   a reactance circuit connected to terminate said second other port, said hybrid thus being arranged to operate in a reflective mode, the characteristics of said reactance circuit being selected relative to the characteristics of said varactor diode such that the loading provided thereby is unbalanced for input signals of a predetermined amplitude and is balanced for input signals of a relatively higher amplitude; and   a circulator coupled to said input port for feeding said input signal to said hybrid and for feeding reflected energy, forming said output signal, away from said hybrid.   
     
     
       5. The system according to claim 4 further comprising a second varactor diode connected to said circulator on the input side thereof to limit said input signal. 
     
     
       6. In a circuit for receiving an input signal and for providing an output signal having stronger portions corresponding to weaker portions of the input signal and having weaker portions corresponding to stronger portions of the input signal, the combination comprising: a power divider having an input port for receiving the input signal and first and second other ports;   a power-responsive balance circuit including first and second circuit channels respectively including first and second quadrature hybrid circuits each having an input port respectively coupled to the first and second other ports of said power divider, said first quadrature hybrid having first and second other ports each terminated by a back-biased diode and further having an output port, said second quadrature hybrid having first and second other ports each terminated by a varacter diode and further having an output port; and   power combining means coupled to said output ports of said first and second quadrature hybrids for providing said output signal.   
     
     
       7. A system according to claim 6 further comprising first and second varactor diode limiters each respectively coupled to the input ports of said first and second quadrature hybrids. 
     
     
       8. A system for receiving an rf input signal and transmitting an rf output signal of the same frequency comprising in combination: quadrature hybrid circuit means connected to receive said input signal and to generate said output signal in response thereto: and   loading means provided at at least two ports of said quadrature hybrid circuit means, said loading means constructed and arranged such that the relative loading at said two ports is unbalanced for input signals of a predetermined amplitude and is balanced for input signals of a relatively higher amplitude whereby the amplitude of said output signal is varied inversely with respect to the amplitude of said input signal.   
     
     
       9. A system for receiving an rf input signal and transmitting an rf output signal in response thereto comprising in combination: signal dividing means for dividing said input signal into first and second divided input signals;   first quadrature hybrid circuit means connected to receive said first divided input signal and operable to shift the phase of said signal by substantially a constant amount;   second quadrature hybrid circuit means connected to receive said second divided input signal and operable to shift the phase of said signal by an amount dependent on the amplitude of said signal; and   means for combining said phase shifted signals to provide an output signal having a frequency equal to the frequency of said input signal and having an amplitude varying inversely with respect to the amplitude of said input signal.